The 4x9x4 Flanged Metal (F684ZZ) Halo series of bearings are a high quality steel/chrome bearing with metal shields. These bearings have been tested and proven by many racers.
Bearing Dimensions
METRIC: 4mm (Inner) x 9mm (Outer) x 4mm (Width)
STANDARD: 0.15748" (Inner) x 0.35433" (Outer) x 0.15748" (Width)